A new NASA and university analysis of ocean data collected more than 135 years ago by the crew of the HMS Challenger oceanographic expedition provides further confirmation that human activities have warmed our planet over the past century.
Researchers from the University of Tasmania, Sandy Bay, Australia; and NASA’s Jet Propulsion Laboratory, Pasadena, Calif., combined the ship’s measurements of ocean temperatures with modern observations from the international Argo array of ocean profiling floats. They used both as inputs to state-of-the-art climate models, to get a picture of how the world’s oceans have changed since the Challenger’s voyage.
The Challenger expedition, from 1872 to 1876, was the world’s first global scientific survey of life beneath the ocean surface. Along the way, scientists measured ocean temperatures, lowering thermometers hundreds of meters deep on ropes.
“The key to this research was to determine the range of uncertainty for the measurements taken by the crew of the Challenger,” said Josh Willis, a JPL climate scientist and NASA project scientist for the upcoming U.S./European Jason-3 oceanography satellite, scheduled to launch in 2015. “After we had taken all these uncertainties into account, it became apparent that the rate of warming we saw across the oceans far exceeded the degree of uncertainty around the measurements. So, while the uncertainty was large, the warming signal detected was far greater.”
Uncertainties around the Challenger’s measurements were caused by the limited areas measured during the voyage; the actual depths the thermometers descended to; and the likely natural variation in temperature that could occur in each region during the voyage.
“Our research revealed warming of the planet can be clearly detected since 1873 and that our oceans continue to absorb the great majority of this heat,” said researcher and lead author Will Hobbs of the University of Tasmania’s Institute for Marine and Antarctic Studies and the Australian Research Council’s Centre of Excellence for Climate System Science. “Currently, scientists estimate the oceans absorb more than 90 percent of the heat trapped by greenhouse gases, and we attribute the global warming to anthropogenic (human-produced) causes.”
The Challenger expedition measurements also revealed that thermal expansion of sea water caused by global warming contributed about 40 percent of the total sea level rise seen in tide gauges from 1873 to 1955. The remaining 60 percent was likely to have come from the melting of ice sheets and glaciers. Prior to this research, climate models offered the only way to estimate the change before the 1950s.
Results of the study are published in the journal Geophysical Research Letters.
For more on the study, visit: imas.utas.edu.au .
Expect more water to lap at your shores. That’s the take-home message from two studies out this week that look at the latest data on sea level rise due to climate change.
The first shows that current projections for the end of the century may seriously underestimate the rise in global sea levels. The other, on the ice sheets of Greenland and Antarctica, looks at just how much of the water stored up there has been moving into the oceans.
Both demonstrate that global warming is a real and imminent threat.
An international research team studied ancient plants from Iceland and Canada, and sediments carried by glaciers.
They say a series of eruptions just before 1300 lowered Arctic temperatures enough for ice sheets to expand.
Writing in Geophysical Research Letters, they say this would have kept the Earth cool for centuries.
The exact definition of the Little Ice Age is disputed. While many studies suggest temperatures fell globally in the 1500s, others suggest the Arctic and sub-Arctic began cooling several centuries previously.
The global dip in temperatures was less than 1C, but parts of Europe cooled more, particularly in winter, with the River Thames in London iced thickly enough to be traversable on foot.
What caused it has been uncertain. The new study, led by Gifford Miller at the University of Colorado at Boulder, US, links back to a series of four explosive volcanic eruptions between about 1250 and 1300 in the tropics, which would have blasted huge clouds of sulphate particles into the upper atmosphere.
These tiny aerosol particles are known to cool the globe by reflecting solar energy back into space.
The Little Ice Age saw an increase in cold winters in parts of Europe, but a small global change
“This is the first time that anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,” said Dr Miller.
“We have also provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time.”
The scientists studied several sites in north-eastern Canada and in Iceland where small icecaps have expanded and contracted over the centuries.
When the ice spreads, plants underneath are killed and “entombed” in the ice. Carbon-dating can determine how long ago this happene